The present invention relates to jaw crushers for crushing aggregate material and having a stationary crushing jaw and a moveable crushing jaw. More specifically, the present invention relates to an improved jaw face for use on the stationary jaw and/or the moveable jaw.
A typical jaw crusher includes a stationary jaw and a moveable jaw that are spaced apart to define a crushing chamber in between. Aggregate material is fed into the crushing chamber and is crushed by cooperating surfaces on each of the jaws as the moveable jaw repeatedly reciprocates toward and away from the stationary jaw.
Typically, the crushing surface of one or both of the jaws will have vertically oriented teeth which run generally parallel to the flow of material through the crushing chamber. Each tooth on each of the jaws is aligned with a corresponding tooth space or valley on the other jaw, such that the material in the crushing chamber is crushed or broken as the material is compressed between the alternating teeth on the face of the jaws. This type of crushing is commonly referred to as cleavage or compression cleavage crushing.
Due to the tremendous forces experienced by the jaw faces, many jaws are manufactured of a heat treated, high manganese content steel casting. During the crushing process, and depending on the angle between the jaws when the jaws are in their closest position, commonly referred to as the nip angle, some portions of the jaw faces may wear much faster than other portions of the jaw faces. For example, for relatively large nip angles, material entering the crusher will quickly fall to the bottom of the crushing chamber, and the bottom portion of the jaw faces will tend to wear faster than the top portion of the jaw faces. Consequently, the faces of one or both of the jaws will be symmetrical, such that the jaws can be removed, turned over, and reinstalled in order to prolong the life of the jaws.
If the nip angle is too large, the material is not gripped by the jaws, and the jaws may actually spit the material out of the contact zone or, in extreme cases, completely out of the crusher. Most crushers will have a maximum nip angle which cannot be exceed in order to avoid material rejection. The maximum nip angle may change depending on the type and shape of various materials. For example, hard, generally spherical alluvial rock will typically dictate a lower maximum nip angle. Further, the angle between the jaw teeth must be kept to a minimum in order to avoid wedging of material between the teeth.
Depending on the desired nip angle between the jaws, which as outlined above may depend on a variety of factors including the type and shape of the material to be crushed, the lower portion of the jaw face may wear significantly faster than the middle portion and the upper portion. Although the jaws can be turned over as mentioned above, other approaches exist which are designed to even out the wear patterns thereby extending the life of the jaws. The most commonly employed approach is to make the profile of the jaw face in the form of a circular arc. Such jaws are commonly referred to as xe2x80x9cbelliedxe2x80x9d jaws. On such jaws, the teeth protrude outwardly at the center of the jaw face, following the profile of an arc having a large radius. This approach reduces the size of the crushing chamber and causes smaller material to be crushed toward the top of the crushing chamber, thus altering the wear patterns.
However, this approach also lowers the nip angle in the lower portion of the crushing chamber, while increasing the nip angle in the upper portion of the crushing chamber. The increased nip angle at the upper portion of the crushing chamber causes problems when crushing larger material sizes, such as the harder generally spherical materials mentioned above.
Accordingly, there exists a continuing need for improvements in the design of jaws for use in jaw crushers.